At first glance, the 32 panels on top of a grocery store in Stockton, California look like solar panels. But this installation is designed not to harness the sun, but to defy it. Coated with a film technology that reflects radiation from the sun, the panels &#; and whatever lies beneath them &#; can drop to 15F (8C) below the ambient temperature, even in the middle of the day, with no electricity required.
It is &#;a fundamentally different way of achieving cooling and harnessing an untapped renewable resource&#;, said George Keiser, chief operating officer of SkyCool, the company behind the panels, which are glazed in a multilayer optical film developed by 3M. &#;We&#;re using the sky as this enormous heat sink,&#; said Keiser, sending excess heat from the surface of the Earth, through the atmosphere and into outer space.
At the grocery store, the panels are used to cool water running behind them, which is then piped into the condensers that run the store&#;s refrigerators. That lowers the temperature of the refrigerants inside, increasing efficiency and reducing yearly energy consumption by 15%.
3M&#;s film has also been applied directly on bus shelters in Tempe, Arizona, to keep commuters cool as they wait.
&#;The long-term goal is to see if we can come up with ways to use either the films or the panels to replace an air conditioner,&#; said Eli Goldstein, the startup&#;s co-founder and chief executive.
SkyCool&#;s cooling panels on a southern California grocery store roof.
Photograph: SkyCoolExtremely hot weather kills about 700 people in the US each year &#; more than hurricanes and floods combined &#; and an estimated 356,000 around the world.
Air conditioning is the most obvious immediate response to the dangerous warming of the planet. It&#;s also making it worse.
Air conditioners use more electricity than any other appliance in the home. They consume 10% of global electricity (together with electric fans) and leak potent planet-warming gases into the atmosphere. On the hottest day of the year in some parts of the US and the Middle East, 70% of peak residential electricity demand is for cooling spaces.
As global temperatures rise and heatwaves become more common and more deadly, the demand for air conditioners is increasing, especially in emerging economies such as India, China and Indonesia.
The International Energy Agency (IEA) estimates that global demand for space cooling will more than triple by . The growing cooling demand is &#;one of the most critical energy issues of our time&#;, according to the IEA&#;s report, which concludes that to keep people cool without spiraling energy demand, the answer &#;first and foremost&#; is to improve the efficiency of air conditioners.
But that&#;s not all it will take. To temper the effects of dangerous heat without heating up the world even more will require a spectrum of solutions, from more efficient ACs to shadier streets, to new technologies that fundamentally change the way we stay cool.
New trees planted along the Valley Metro Rail in Phoenix, Arizona. There is minimal shade in the neighborhood and the heat can be 20F hotter than in other parts of the Phoenix metro area.
Photograph: Caitlin O&#;Hara/The GuardianMost ACs are relatively cheap and extremely inefficient. The energy performance standards the machines are required to meet don&#;t come close to maximizing their potential, said Iain Campbell, senior fellow at the sustainability nonprofit Rocky Mountain Institute, and 95% don&#;t exceed the bare minimum.
Another big problem with air conditioners is that they leak hydrofluorocarbon refrigerants (HFCs), powerful planet-warming gases and a major contributor to global heating, into the atmosphere. The most commonly used &#; R-410A &#; is more than 2,000 times more potent than carbon dioxide.
As the machines work, the refrigerant travels in tubes between areas of low and high pressure, turning into a gas as it absorbs heat from inside and releases the heat outside as it condenses back into a liquid. In its gas form, HFCs can seep out through joints in the piping (a typical residential unit might lose 10% of its refrigerant each year) or can be released entirely if an air conditioner is thrown away without being properly drained.
In , the Rocky Mountain Institute launched the Global Cooling prize, offering a $1m prize for new residential cooling technology that is five times more efficient and less polluting than today&#;s standard machines, costs no more than twice as much for consumers and can be installed in existing homes.
The two winning prototypes, announced in April and produced by two of the world&#;s largest cooling manufacturers &#; Daikin and Gree &#; work fundamentally the same way as today&#;s air conditioners, but are engineered with better sensing and controls and are configured to use more environmentally friendly refrigerants than those found in standard residential AC units. They have also added features, such as engineering to remove excess moisture from the air to make it easier to cool (it takes more energy to heat humid air).
The winners say they will bring their designs to market by . But until policymakers in the US and abroad raise the floor on efficiency standards for AC units, said Campbell, there&#;s no clear way for consumers to discern the difference between these new machines and those that are less efficient and have a far greater climate impact.
Mechanical engineer Vince Romanin realized that few consumers research air conditioner efficiencies or specific refrigerants before buying, which is why he markets his AC technology on user experience, rather than environmental credentials.
&#;There are about 50 million people in the US with a window AC, and almost all of them hate them,&#; said Romanin, CEO of Gradient. Configured to straddle the window sill, with the noisy bits outside and the tech housed below the window, Gradient&#;s machine is not &#;loud and ugly&#;, said Romanin, and it doesn&#;t block your view.
Gradient uses a lower-emissions refrigerant packed in factory-sealed, leak-proof tubing. Coming to market next year, it&#;s two appliances in one: the heat pump system that replaces hot air with cool in the summer works in reverse to make it a space heater in the winter.
Gradient&#;s AC machines straddle the window sill and promise more efficient, less climate damaging technology.
Photograph: GradientCampbell is excited about the potential of new materials to push cooling technology even further. Cooling prize finalist Transaera is developing a &#;novel sponge-like&#; material that could improve air conditioners&#; efficiency by passively sucking moisture out of the air. But until governments impose standards that rate ACs on how efficiently they reduce humidity, Campbell said, manufacturers lack incentive to include the tech in their products.
Irish clean tech company Exergyn is among those developing systems that replace harmful, leaky refrigerants with solid materials that contract and relax as they absorb and release heat. Solid state refrigerants have &#;significant promise&#;, Campbell said, but they need more testing to prove they can last as long.
Better air conditioners alone can&#;t solve the growing heat crisis, but they&#;re an important part of the puzzle, said Campbell, especially for the growing urban populations around the world.
There are many other things you&#;d ideally do first, he said. That includes designing buildings that use less energy, have better ventilation and are better insulated from heat.
&#;If you want to cool people, you have to provide shade, period,&#; said V Kelly Turner, assistant professor of urban planning at UCLA&#;s Luskin School of Public Affairs. Whether that&#;s in the form of trees or canopies, people&#;s bodies need to be protected from the direct heat of the sun.
There&#;s also the indirect effect of the sun heating physical surfaces, such as streets and buildings. In cities, where the urban heat island effect can raise the temperature by as much as 20F (12C), the simple act of painting roofs white can reflect enough sunlight to reduce the heat by a few degrees.
A dozen US cities require or encourage light-colored roofs on new construction, and in August dark roofs were banned in the south-west suburbs of Sydney, Australia, where new rules mandate that every backyard must have a tree.
It&#;s necessary to tackle the fundamental problems that make cities hotter, said Turner. But &#;we will need some air conditioning because [without it], you can&#;t get your core temperature cool enough if you&#;re exposed to really extreme heat&#;. That&#;s especially important, she stressed, for vulnerable people, including outdoor agricultural and construction laborers, children, elderly people and low-income renters, who need not only access to cooling centers on the hottest days, but air conditioning in their homes. (Most places in the US, she said, have laws limiting how cold an apartment can be, but none that prevent landlords from letting homes get dangerously hot.)
People at a cooling center at Kellogg middle school in Portland, Oregon.
Photograph: Michael Hanson/AFP/Getty ImagesThe Cooling prize targets air conditioning &#; that last, necessary element. &#;If your living space is a very small apartment in a mid-rise tower and you have six members of the family living there and the temperature in the summer is peaking out at about 120F, 130F, you&#;re not gonna say: &#;Well I need to insulate my apartment, or I need to put some shading in,&#;&#; said Campbell. &#;You&#;re thinking, &#;I need a damn conditioner so we can all sleep at night.&#;&#;
People are going to keep buying air conditioners, he said, so we need to offer them better, safer, cleaner devices &#; and policymakers must impose regulations that take less efficient options off the table: &#;We can do better than this. And we&#;re doing a disservice to our citizenry when we let them buy something that is so expensive to operate, and so polluting that cooling is actually adding to the warming of the planet.&#;
This article was amended on 16 September to make clear the role of 3M in the film used on SkyCool&#;s panels.
The main purposes of a Heating, Ventilation and Air-Conditioning (HVAC) system are to help maintain good indoor air quality (IAQ) through adequate ventilation with filtration and provide thermal comfort. HVAC systems are among the largest energy consumers in schools. The choice and design of the HVAC system can also affect many other high performance goals, including water consumption (water cooled air conditioning equipment) and acoustics.
The following actions detail how engineers can design a quality system that is cost-competitive with traditional ventilation designs, while successfully providing an appropriate quantity and quality of outdoor air, lower energy costs and easier maintenance.
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The national consensus standard for outside air ventilation is ASHRAE Standard 62.1-, Ventilation for Acceptable Indoor Air Quality and its published Addenda. This standard is often incorporated into state and local building codes and specifies the amounts of outside air that must be provided by natural or mechanical ventilation systems to various areas of the school, including classrooms, gymnasiums, kitchens and other special use areas.
Many state codes also specify minimum energy efficiency requirements, ventilation controls, pipe and duct insulation and sealing and system sizing, among other factors. In addition, some states and localities have established ventilation and/or other IAQ related requirements that must also be followed.
Standards are available at ASHRAE.
In some parts of the country, where temperature and humidity levels permit, natural ventilation through operable windows can be an effective and energy-efficient way to supplement HVAC systems to provide outside air ventilation, cooling and thermal comfort when conditions permit (e.g., temperature, humidity, outdoor air pollution levels, precipitation). Windows that open and close can enhance occupants' sense of well-being and feeling of control over their environment. They can also provide supplemental exhaust ventilation during renovation activities that may introduce pollutants into the space.
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However, sealed buildings with appropriately designed and operated HVAC systems can often provide better IAQ than a building with operable windows. Uncontrolled ventilation with outdoor air can allow outdoor air contaminants to bypass filters, potentially disrupt the balance of the mechanical ventilation equipment and permit the introduction of excess moisture if access is not controlled.
Strategies using natural ventilation include wind driven cross-ventilation and stack ventilation that employs the difference in air densities to provide air movement across a space. Both types of natural ventilation require careful engineering to ensure convective flows. The proper sizing and placement of openings is critical and the flow of air from entry to exit must not be obstructed (e.g., by closed perimeter rooms).
In most parts of the country, climatic conditions require that outdoor air must be heated and cooled to provide acceptable thermal comfort for building occupants, requiring the addition of HVAC systems. The selection of equipment for heating, cooling and ventilating the school building is a complex design decision that must balance a great many factors, including:
Where feasible, use central HVAC air handling units (AHUs) that serve multiple rooms in lieu of unit ventilators or individual heat pumps. Although there are many different types of air handling units, for general IAQ implications in schools, air handling units can be divided into two groups: unit ventilators and individual heat pump units that serve a single room without ducts; and central air handling units that serve several rooms via duct work.
Unit ventilators and heat pumps have the advantage of reduced floor space requirements and they do not recirculate air between rooms. However, it is more difficult to assure proper maintenance of multiple units over time and they present additional opportunities for moisture problems through the wall penetration and from drain pan and discharge problems. Central air handling units have a number of advantages as compared to unit ventilators and heat pumps serving individual rooms, including:
Double-Sloped Drain Pan and Drain Trap Depth
Indoor air can be two to five times more polluted than outdoor air; therefore, most HVAC system designers understand that increased amounts of outdoor air supply is generally better for IAQ. Yet there are concerns over the implications that this added amount of outdoor air supply has on the first cost and operating cost of the HVAC system, as well as moisture control for the school (too wet or too dry).
As a result, school designers often try to reduce the amount of outdoor air equal to &#; or even below &#; 15 cubic feet per minute (cfm) of outside air per person, the minimum for school classrooms, as established by the American Society of Heating, Refrigerating and Air -conditioning Engineers (ASHRAE) ASHRAE. In many parts of the country these concerns can easily be addressed by application of basic engineering principles and off-the-shelf HVAC equipment.
First cost, energy costs and moisture control do not have to be at odds with good IAQ. Energy recovery ventilation equipment can make the negative implications of 15 cfm per person of outdoor air behave like 5 cfm, while retaining the IAQ advantage of 15 cfm. This approach has been proven in many schools in various regions east of the Rockies, where advanced HVAC systems cost roughly the same as conventional systems, yet provide significant operating cost savings and IAQ advantages.
Classrooms and other school spaces must be ventilated to remove odors and other pollutants.
If outside air is provided through a mechanical system, then at least 15 cubic feet per minute (cfm) of outside air must be provided for each occupant. A typical classroom with 30 people requires a minimum of 15 x 30 or 450 cfm of outside air.
In spaces where the number of occupants is highly variable such as gyms, auditoriums and multipurpose spaces, demand controlled ventilation (DCV) systems can be used to vary the quantity of outside air ventilation in these spaces in response to the number of occupants. One technique for doing this is to install carbon dioxide (CO2) sensors that measure concentrations and vary the volume of outside air accordingly.
If an auditorium fills up for school assembly, then CO2 concentrations will increase, a signal will be provided to the HVAC system and outside air volumes will be increased accordingly. When the spaces served by an air handler have highly variable occupancy, this type of control can both save energy and help control moisture (and mold) by reducing the quantity of humid outside air when it is not needed for ventilation. CO2 and other sensors must be periodically calibrated and maintained.
In addition to "atmospheric dust," airborne particulates can include pollen, mold (fungal) spores, animal dander, insect proteins, pesticides, lead and infectious bacteria and viruses. Designers can integrate features into the ventilation system that will provide benefits for the school occupants as well as the efficiency and longevity of the HVAC system. In addition, these features can reduce the need for expensive cleaning of the duct work and air handling units.
The most effective means of reducing exposure of occupants to gases and VOCs is to manage and control potential pollution sources. Filters are available to remove gases and volatile organic contaminants from ventilation air; however, because of cost and maintenance requirements, these systems are not generally used in normal occupancy buildings or schools. In specially designed HVAC systems, permanganate oxidizers and activated charcoal may be used for gaseous removal filters.
Some manufacturers offer "partial bypass" carbon filters and carbon impregnated filters to reduce volatile organics in the ventilation air of office environments. Gaseous filters must be regularly maintained (replaced or regenerated) in order for the system to continue to operate effectively.
Although a typical HVAC system has many controls, the control of outdoor air quantity that enters the building can have a significant impact on IAQ, yet typically is not part of standard practice. Demand controlled ventilation is addressed as a method of humidity control, but is not otherwise discussed here because its primary use is to reduce the supply of outdoor air below the recommended minimum for the purposes of saving energy, not for improving IAQ.
Supplying acceptable quantities of outdoor air to occupied spaces is a critical component of good IAQ. Yet nearly all school ventilation systems cannot indicate whether outdoor air is even being supplied to the school, much less gauge the quantity of that air. Virtually all existing school ventilation systems rely upon a fixed damper to regulate the amount of outdoor air.
Yet wind, stack effect, unbalanced supply and return fans and constantly changing variable air volume (VAV) systems can cause significant under- or over-ventilation, which can affect IAQ and energy costs. Combinations of these effects can even cause the intake system to actually exhaust air.
Uncontrolled moisture indoors can cause major damage to the building structure, as well as to furnishings and to finish materials like floors, walls and ceilings. Uncontrolled moisture can trigger mold growth which not only damages the school facility, but can lead to health and performance problems for students and staff.
Primary causes of indoor moisture problems in new schools include:
Controlling moisture entry into buildings and preventing condensation are critical in protecting buildings from mold and other moisture-related problems, including damage to building components.
Dirt and moisture should not be present in duct systems and must be controlled to prevent mold growth. However, it is not always possible to assure that ducts remain dirt and moisture free. In many existing schools, sheet metal ducts, as well as those constructed of or lined with insulation products, are often contaminated with mold because dirt and moisture found their way into the system.
Duct board and duct liner are widely used in duct systems because of their excellent acoustic, thermal and condensation control properties. If the HVAC system is properly designed, fabricated, installed, operated and maintained, these duct systems pose no greater risk of mold growth than duct systems made of sheet metal or any other materials.
However, the very properties that make duct board and duct liner superior insulators (e.g., a fibrous structure with large surface area that creates insulating air pockets), also makes them capable of trapping and retaining moisture if they do get wet (though the fibers themselves do not absorb moisture).
While there is an ongoing debate about the wisdom of using insulation materials in duct systems that might retain moisture longer, all sides agree that extraordinary attention to preventing moisture contamination of the duct work should be the primary strategy for preventing mold growth. See ANSI/ASHRAE Addenda 62t and 62w, Addenda to ANSI/ASHRAE Standard 62-, Ventilation for Acceptable Indoor Air Quality.
As a secondary strategy, designers should consider methods of reducing the potential for future problems to occur due to unforeseen moisture contamination by investigating insulation products now on the market that minimize the potential for moisture to penetrate the insulation material. These include foil vapor retarders, tightly bonded non-woven vapor retarders, butt or shiplap edges and other techniques that have been developed by insulation manufacturers to address concerns about moisture.
Nearly all schools currently use the mixed-airflow method for distribution and dilution of the air within the occupied space. Designers should investigate a method called vertical displacement ventilation or thermal displacement ventilation. This approach successfully uses natural convection forces to reduce fan energy and carefully lift air contaminants up and away from the breathing zone.
Quick removal of concentrated air contaminants and building pressurization are two ways that exhaust systems affect IAQ. Special use areas such as science labs, vocational/technical shops, cafeterias and indoor pools already have well established regulatory codes regarding ventilation with outdoor air and negative pressure requirements with respect to adjacent spaces. Less well recognized areas in schools where special exhaust ventilation is desirable are janitor closets, copy/work rooms and arts/crafts preparation areas where off-gassing from significant quantities of materials or products may occur. These areas should be maintained under negative pressure relative to adjacent spaces.
Ensure that all system components, including air handling units, controls and exhaust fans are easily accessible. To help ensure that proper operation and maintenance of HVAC system components will be performed, it is critical that the designer makes the components easily accessible. AHUs, controls and exhaust fans should not require a ladder, the removal of ceiling tiles, or crawling to gain access. Rooftop equipment should be accessible by way of stairs and a full-sized door, not a fixed ladder and a hatch.
Label HVAC system components to facilitate operations and maintenance. Labeling of HVAC components is an inexpensive and effective method for helping facilities personnel properly operate and maintain the HVAC systems. The labels should be easy to read when standing next to the equipment and durable to match the life of the equipment to which they are attached. At a minimum, the following components should be labeled in each ventilation zone of the school and should correspond with the HVAC diagrams and drawings. "AHU" refers to any air handling unit that is associated with outdoor air supply.
The number or name of the AHU (e.g., AHU ##, or AHU for West Wing)The number or name of the AHU (e.g., AHU ##, or AHU for West Wing)
The outdoor air (OA), supply air (SA), return air (RA) and exhaust or relief air (EA) connections to the AHU, each with arrows noting proper airflow directionThe outdoor air (OA), supply air (SA), return air (RA) and exhaust or relief air (EA) connections to the AHU, each with arrows noting proper airflow direction
The access door(s) for the air filters and the minimum filter dust-spot (or MERV) efficiency (Air Filters, minimum xx% dust spot efficiency)The access door(s) for the air filters and the minimum filter dust-spot (or MERV) efficiency (Air Filters, minimum xx% dust spot efficiency)
The filter pressure gauge and the recommended filter change pressure (Filter Pressure, max 0.x in. w.g.)The filter pressure gauge and the recommended filter change pressure (Filter Pressure, max 0.x in. w.g.)
The access door(s) for the condensate drain pan (Drain Pan)The access door(s) for the condensate drain pan (Drain Pan)
Other pertinent access doors such as to energy recovery ventilation wheels or plates (Energy Recovery Ventilation Unit)Other pertinent access doors such as to energy recovery ventilation wheels or plates (Energy Recovery Ventilation Unit)
The minimum amount of outdoor air for each AHU (### CFM minimum during occupied times)The minimum amount of outdoor air for each AHU (### CFM minimum during occupied times)
The outdoor air damper (OA Damper), with special marks noting when the damper is in the fully closed (Closed), fully opened (open) and minimum designed position (Min)The outdoor air damper (OA Damper), with special marks noting when the damper is in the fully closed (Closed), fully opened (open) and minimum designed position (Min)
If a motorized relief damper is installed (EA Damper), note the same positions as above.If a motorized relief damper is installed (EA Damper), note the same positions as above.
The access door to any outdoor air controls (OA Control(s)) such as damper position adjustments, outdoor airflow measuring stations, resets, fuses and switches)The access door to any outdoor air controls (OA Control(s)) such as damper position adjustments, outdoor airflow measuring stations, resets, fuses and switches)
Breakers for exhaust fans (Exhaust Fan ##), AHU, unit ventilatorsBreakers for exhaust fans (Exhaust Fan ##), AHU, unit ventilators
Access doors for inspection and maintenance of air ductsAccess doors for inspection and maintenance of air ducts
Any dampers and controls for air side economizers (as appropriate)Any dampers and controls for air side economizers (as appropriate)
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